When computers first started displaying graphics, the visual graphics were rudimentary. They tended to be limited to lines and then combinations of lines and blocks. Over time, the capability of computers to display graphics has increased significantly. Computers can now display three-dimensional (3D) graphics with realistic-looking surfaces.
In fact, computer-generated graphics are becoming more and more realistic. One approach to generating realistic-looking graphics involves accurately mimicking the behavior of light as it propagates through a graphical scene, including with respect to surfaces. The result can be impressive compared to the rudimentary lines and blocks of the past. Unfortunately, accurately mimicking light propagation behavior within a graphical scene is computationally intensive. Consequently, there are formidable barriers to displaying real-world lighting effects in real-time.